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Throttling for all cross-origin iframes that are
This article describes iframe throttling and the benefits of standardizing throttling for display: none and non-visible.
Note
This article applies to Microsoft Edge version 116 or later.
Summary
Cross-origin iframes that are display: none and non-visible are throttled when rendered cross-process, but not when they're rendered same-process. The absence of throttling in same-process scenarios could lead to unpredictable behavior for developers, who might not know the underlying process model used to render the page. Also, with this iframe scenario, a malicious actor can probe to see whether a browsing session has site/origin isolation enabled.
Throttled iframes lose access to requestAnimationFrame and ResizeObserver, so the different throttling approaches affect web developers. This feature standardizes throttling, so it applies to all cross-origin iframes, regardless of whether they're same-process or cross-process.
Note
"non-visible" means a non-zero area frame that's outside the viewport.
Objective
Iframe throttling is a Blink mechanism that tries to reduce layout and rendering overhead. Frames that are throttled only undergo partial layout, and requestAnimationFrame and ResizeObserver don't operate when a frame is throttled. Cross-origin iframes that are placed in a different process than their parent, and that are either display: none or non-visible are throttled. Currently a cross-origin frame that's rendered in the same-process as its parent isn'tthrottled, leading to different behavior based on a process model. When enabled, this policy throttles all cross-origin, display: none or non-visible frames, which gives consistent behavior between the same-process and cross-process cases.
Content license
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Portions of this page are modifications based on work created and shared by Chromium.org and used according to terms described in the Creative Commons Attribution 4.0 International License. The original page can be found here.
This work is licensed under a Creative Commons Attribution 4.0 International License.